Method and apparatus for forming of reinforced tube

ABSTRACT

A process and apparatus for producing a ribbed pattern on extruded film by differential cooling of the film during its stretching process. The film is extruded through a tubular film die, stretching as it leaves the die. Cooling mechanisms rotate about the tube as it is being extruded to define a large plurality of narrow strips on the melt as it is being extruded. The film is fixed in space to maintain a close proximity to the cooling mechanisms in order to achieve sharply defined ribs. A cross-ribbed pattern can be obtained by counter-rotating the cooling mechanisms. Increased tear strength is imparted to the film without increasing the amount of resin necessary to make the film. Such tube can be formed into high strength film products such as trash bags and the like.

BACKGROUND OF THE INVENTION

Bags made from thin films tend to zipper or otherwise tear whenpunctured or stressed. It has been long desired to reduce the tendencyof such thin films to zipper and tear without significantly increasingthe bag thickness or weight as required in ribbed bags shown in U.S.Pat. No. 3,193,604, for example. Attempts to accomplish such a desiredresult can be found in U.S. Pat. No. 3,265,789 or British Pat. No.1,250,945 which impinge air on tubular film as it is being extruded.Some amount of thickness is provided by the cooling mechanisms of thesepatents but the mechanisms fail to provide a configuration of ribintensity, sharpness, strength and pattern necessary to maximize thetear strength of the film without significantly increasing the resinrequirements and weight of the film produced. The present inventionprovides a process and apparatus for producing a film havingextraordinary tear strength because of the characteristics imparted tothe film by such process and apparatus.

SUMMARY OF THE INVENTION

The present invention comprises a process whereby tubular film isextruded from a conventional tubular extrusion die across one or moreair bearings to fix the film in position. The extruded tube is stretchedabout two or three to one transversely while simultaneously beingstretched about ten to one or more in the machine direction. Thisimparts a high degree of orientation into the extruded product toincrease its tear strength.

Shortly after the film has formed adjacent the extrusion die, the filmis selectively contacted by a cooling means generally opposite the airbearing to form a plurality of narrow strips or ribs where the melt isselectively cooled more than it is naturally cooled in the process asshown in the aforesaid U.S. Pat. No. 3,976,733. The selective coolingraises the melt tension of the resin in this highly cooled area so thatit does not stretch as much transversely as the adjacent warmer film.This higher melt tension forms a sharp rib in the film body. Acriss-crossed rib pattern of such ribs can be formed by counter-rotatinga plurality of cooling mechanisms providing a built-in link-typeconfiguration. The pattern of sharply defined ribs providessubstantially increased mechanical film toughness without a significantincrease in film weight, or average thickness. Cooling can be providedby impinging upon the extruded film a gas, such as air, a mist, such aswater vapor, or snow. In each case, a mechanism allowing for coolingdevices to carry the mist, gas or snow about the extruded film can beemployed. Alternately, water-wick or metal contact devices can beemployed to provide thickened ribs in a similar pattern about the tubeas it is being longitudinally stretched upon extrusion. A quench mandrelcan aid in speeding up the process where desired. The cooling mechanismscan be located either internally or externally of the extruded tubing toachieve the desired result.

A film not only of increased strength is achieved but also one which canbe multilayered to present a visible rib by use of layers havingcontrasting colors.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a preferred embodiment of theapparatus and process of the invention;

FIG. 2 is an enlarged cross-sectional view of the quench former portionof the apparatus of FIG. 1 taken along reference line 2--2 of FIG. 1;

FIG. 2A is an enlarged view of the cooling nozzles of FIG. 2, takenalong line 2A--2A thereof;

FIG. 3 is a view like FIG. 2 only showing a modified form of theinvention embodying water-wetted wicks;

FIG. 4 is a schematic representation of apparatus like that shown inFIG. 1 only with the cooling mechanism located within instead of outsidethe tubular extrusion;

FIG. 5 is an enlarged view of one of the rings of FIG. 4;

FIG. 6 is yet another modified form of the arrangement shown in FIG. 4;

FIG. 6A is a view of the arrangement of FIG. 6 taken along referenceline 6A--6A thereof;

FIG. 7 is an elevational view, partially broken away, of a two-ply bagmade from the film produced by the process illustrated in FIG. 1; and

FIG. 8 is a cross-sectional view of the bag of FIG. 7 taken alongreference line 8--8 thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is schematically depicted, partly in-section, anapparatus of the present invention generally designated by the referencenumeral 10. This apparatus 10 is basically the apparatus described inU.S. Pat. No. 3,976,733 only modified to perform the function ofextruding a thin film with a rib pattern so as to greatly enhance itstear strength. The preferred pattern is cross-ribbed and the inventionwill be described with that pattern primarily in mind, even though otherpatterns using the principles of the invention may be employed. Manyportions, of the apparatus shown in FIG. 1 herein are like those shown,for example, in FIG. 1 of U.S. Pat. No. 3,976,733 and performessentially the same functions. Principally, an extruder die 12 is fedby one or more resin pipes 14 and 16, depending on the number of layersdesired to be formed. A multilayered die such as shown in U.S. Pat. No.3,354,506 can be employed to form more than one layer, for example. Thispermits obtaining a more visible rib with layers of contrasting colors.

Through the center of the die 12 is a supporting cylinder 18 which isalso a supply means for introducing cooling fluid to upper and lower gasbearings 20 and 22, respectively. These gas bearings provide support forfixing the film in a specific position. A cooling gas means, in the formof a conventional air ring 24, is applied externally of the tubularextrudate or film 26 adjacent the extrusion die orifice 28. A third gasbearing 30 and a tube positioning means 29, the latter being suppliedfrom the gas source 32, are also provided for film control duringcooling. Bearing 30 is supplied with gas in a manner similar to that ofthe bearings 20 and 22. A quenching mandrel 34 can be employed torapidly cool the balance of the film extrudate. A collapsing rack 36,end splitter 38 and take-off rollers 46 are found at the lower end ofthe system of FIG. 1 and function in a manner similar to that describedin the aforesaid U.S. Pat. No. 3,976,733 patent.

Generally adjacent, but located below upper bearing 20 and above lowerbearing 22, are a pair of counter-rotating nozzle ring devices 42 and44, generally circumferential in cross-section in a plane normal to theaxis of extrusion as are the bearings 20 and 22. For example, uppernozzle ring 42 can move clockwise while lower nozzle ring 44 can movecounter-clockwise about the film 26. These ring apparatuses containnozzles 46 for impinging a cooling fluid upon the exterior surfaces ofthe film as it passes thereby. Air bearings 20 and 22 are locatedadjacent upper air ring 24 so that the nozzles 46 can impinge coolingmedium upon the surface of the film at a point where the film hassolidified enough to maintain its body but has not yet solidified beyondits normal forming temperature. The closer the cooling mechanisms are tothe zone in which the film is initially extruded the more affect theycan have in forming the desired cross-patterned rib having increasedthickness. However, the degree of thickness can be adjusted by movingthe nozzle ring apparatus upwardly and downwardly in the machinedirection as desired. Porous air bearing 20 as well as porous airbearing 22 are supplied air through cavity 48 in a conventional manner.This allows the film 26 to pass by the outer surfaces 50 of each of thebearings with a small gap between the bearing and the film so that theair gap 52 provides a slip passage of the film past the air bearings.

The air bearings by being closely adjacent the cooling mechanismsprovide support for the film so that as the cooling means impinges uponor otherwise contacts the film surface, the film does not move away fromthe nozzles and dissipate their effect. Slight increases in the spacingbetween the nozzles and the film can significantly decrease ribsharpness. The air bearings provide controlled film location andcontrolled rib definition as desired. For example, in experimentation ithas been found that the nozzle orifices perform well if the distance Xbetween the squench former face 64 and nozzle face 57 of FIG. 2 is 1 to20 times the gap Y of orifices 60 (FIG. 2A), later described, andpreferably 1 to 10 times the gap.

A liquid can be supplied to the quench former 54 through passageways 56through a water baffle 58, the water baffle providing a more uniformquench-forming temperature. Nozzles 56 are angularly disposed withrespect to the face of the die 28, which will ordinarily be horizontal,at about 45°± about 20°, and emit their cooling means through orifices60 which can, for example, be disposed about 90° from one another asshown in FIG. 2A. Coolants supplied through channels 62 supply theorifice 60, which fluid impinges upon the outer surface of film 26 topush it against the surface 64 of quench former 25 so that a pronouncedsharp rib effect is achieved. Otherwise the film is spaced from surface64.

A modified form of the rib forming apparatus of the present invention isfound in the cross-section of FIG. 3, the principle difference betweenthis apparatus and that described with respect to FIG. 2 being that thequench former 25 has been removed and instead of nozzles blowing acoolant against the exterior film, water-wetted wicks 68 and 70 contactthe surface of film 26 at locations 72 and 74. The wicks severely coolthe film at such contact areas to form an extra-sharp cross-rib patternwhere desired. Water wetted wicks 68 and 70 are carried bycounter-rotating wick ring apparatuses 76 and 78 which are rotated byany well known means, not shown, and are supplied by a fluid deliverysystem engaged directly with the wicks through channels 80 in anyconvenient manner as can be developed by one skilled in the art. Again,air bearings 20 and 22 fix the film in position so that the location ofcooling wicks 68 and 70 can be maintained with respect to the filmsurface. In this case, the fluid 81 contained in the wicks is in directcontact with the film surface.

Yet another modified form of the present invention is that shown in FIG.4. FIG. 4 is somewhat like FIG. 1 only internal cooling mechanisms areemployed and an extra air bearing 92 for added support is located inthis modified system 90.

In the embodiment shown in FIG. 4, spaced internal air or coolant rings94 and 96 are located between bearings 20 and 22. These rings beingessentially in the location of the quench former 25 of apparatus 10. Theinternal air rings 94 and 96 are also counter-rotating so as to providean internal cross-ribbed effect on the tube. The rings are circular inplan view. One such ring is shown in expanded detail in FIG. 5. Thenozzles 98 shown in this view are angled at about 60° in this particularembodiment to the face of the die 28, the angle determining the width ofthe rib formed on the internal surface 100 of the film 26.

The bearings 20 and 22, with tension supplied to the film 26 by take-offrollers 46, maintain the film in a spaced location from the nozzles 98so that the film distance to provide sharp ribs is achieved.

Yet another modified form of the present invention is shown in FIGS. 6and 6A where instead of cooling nozzles 46, narrow slits 102 and 104 areformed through a pair of porous glass bearings 106. This permits a highvelocity of air passage through the slits, while the rest of thebearings act in a customary way to locate the film and form an air slip.In such case, one can expect the ribs to be wider and not as pronouncedas in the embodiment of FIG. 5. In all other respects, however, thefunction of the apparatus of FIG. 6 is like that in FIG. 5.

The present invention has been operated successfully, producing ribs bycooling with air, air/water mist, ice, dry ice, metal shoes, and byusing an air nozzle to force the film against a smooth quench former asis illustrated particularly in FIG. 1, for example. This last methodgives dual cooling, both the air and the quench former contributing tothe cooling of the rib.

Basically, thermoplastic tube or film 26 is extruded over one or moreair bearings 20, 22, and 30, with the tube being only partially expandedat the location where the cooling means for generating the ribs on thefilm is operating. In the case where only cooling air is used, forexample, an air bearing can be located in place of the cooling mandrel25 of FIG. 1. This is particularly true where more accentuated ribsand/or high extrusion rates are not critical.

The ribs are generated by blowing a narrow stream of gas, mist, or snowat a high velocity against the film as it passes over an air bearing orquench former. This cools a narrow strip of film reducing its tendencyto stretch in the transverse direction. The result is the thickened webin the film. In each case, whether cooling with a gas, a water mist, orsnow formed by ice or dry ice, certain design or process parameters havebeen determined to provide the desired result. The exit nozzle 46 may beround, rectangular or curved. The nozzle gap or diameter 60 may be from0.005 inch to 0.050 inch with the preferred range being 0.010 inch to0.030 inch. The nozzle 46 may be perpendicular to the surface film 26 orit may be 10 to 40 degrees off perpendicular, giving a sharp thicknessincrease on one edge and a gradual increase on the other edge of therib. The clearance between the nozzle 46 and the film 26 may be 0.050inch to 0.300 inch with preferred range being 0.10 inch to 0.15 inch.The spacing between nozzles 46 may range from 0.3 inch to 3.0 incheswith the preferred range being 0.60 inch to 1.5 inches.

The expansion of the tube at the nozzles 46 should be in the range of-10% (due to necking in) to 75% of the total expansion, with thepreferred range being (-10%) to 25% of the total expansion to obtain thegreatest rib sharpness or definition. It is desirable to contact thefilm with the cooling means before the film expands too far. Nozzles 46may be stationary and oriented vertically for producing vertical ribs orset at opposed 45° or another angle and counter-rotated to generate amesh film pattern. Optionally, the nozzles 46 may be internal as shownin FIG. 4 with an external air bearing (not shown), if desired. Asimpler system employing a single air bearing in place of the sandwichcomprising an air bearing/water cooled mandrel/air bearing, asillustrated in FIG. 1 may be used. However, with the omission of themandrel, supplementary cooling for the ribs is lacking, resulting inless production rate capability. For increased sharpness, a pair ofnozzles with an included angle of about 90-120 degrees may be used inplace of each nozzle 46, the air tending to exit between the nozzles toconcentrate the multiple coolant flow to the rib zone on the film. Thecooling methods of this invention may also be applied to a simple blownfilm process as well as the process taught in U.S. Pat. No. 3,976,733.

FIGS. 2 and 2A illustrate in more detail the operation of the inventionwhere a liquid-cooled mandrel is used. Here air enters through cavities48 through bearings 20 and 22 to push the inner surface of the film awayfrom outer surface 50 of each bearing so as to establish air slip gap 52therebetween. As the film passes by cooling mandrel 54, its outersurface 64 is contacted by the film directly opposite exit orifice 60 ofthe nozzles which causes the film to contact the cooling mandrel as itis extruding downwardly past lower bearing 22. Coolant liquid such ascooled water, passes through channels 56 and passage 58 to provide theincreased coolant effect necessary for the rapid cooling to occur. Whilethe film is passing by the nozzles, the nozzles, which are carried bycircumferential rings 42 and 44, rotating counter to one another, formthickened ribs in the surface of film 26 which criss-cross one anotheras the film is extruded down past lower bearing 22.

An illustration of the criss-cross pattern can be found not onlygenerally on FIG. 1 but in more detail in the embodiment of FIGS. 7 and8. The diamonds formed by the ribs when initially formed near thebearing 20 take on a much different shape and size as the tube expandsover bearing 30. The diamond-shape expands laterally and longitudinallyas the film is expanded and in about the same proportion. Since the tubeis expanded much more in the longitudinal (machine) direction than thelateral (transverse) direction, the diamond 101 will become relativelymuch taller than when initially formed as diamond 99. The center of thediamond will become thinner upon expansion but will not significantlylose its toughness because it becomes highly oriented sincesubstantially all of the expansion occurs in the material between theribs. Any tearing in the center of the diamond will customarily stop ata rib rather than continue to zipper through the film body. FIG. 7 showsa bag 110 having criss-cross parallel ribs 112 and 114 having a profileB and which cross at point A. Ribs 112, for example, could be formed bythe nozzles 46 carried by rotating ring 42 and the ribs 114 could beformed by the nozzles 46 carried by oppositely directed ring 44. Thethickness B of the rib, if the film were given a unit of one, forexample, could be 2, and at a cross-rib the thickness A could be 3.Specific thicknesses can be found in Table I, for example, where sampleswere compared with a Control F2-1 having a nominal thickness at aboutthe same as each of the samples of F2-2, J-2 and F4.1. The "X-Rib"section of the samples are equivalent to the thickness A on FIGS. 7 and8, the "Rib" is comparable to the thickness B shown at ribs 112 and 114of the drawing and the "Diamond" being that portion of the film 110between the ribs, as expanded, and shown in FIG. 7. The machinedirection and transverse direction, tear strength as measured using aElmendorf tester, typically shows the increased strength achieved bypractice of the present invention. These results were obtained usingonly air cooling against an air bearing. Considerably improved resultscan be obtained using supplemental cooling means as with a water-cooledmandrel of FIGS. 1 and 2 or water wicks or metal shoes, later described,as contemplated by the embodiment of FIG. 3, for example. Cooling with aquench former, with an air nozzle 10 as illustrated in FIG. 1, forexample, can be about ten fold over that found with just air nozzlesalone. If the air is replaced with an air water mist, the improvementcan be in the magnitude of 30 fold. If water cooling is achieved withmoistened wicks as taught in the embodiment of FIG. 3, for example, theimprovement can be 50 fold or more.

                                      TABLE I                                     __________________________________________________________________________    Sample                                                                            Gauge - Mils     Tear-gms                                                                            Rate Nozzles                                       No. Nom.                                                                              X-Rib                                                                              Rib                                                                              Diamond                                                                            Md Td Lbs/Hr                                                                             Rpm                                                                              Psi                                                                             Air fpm                                                                            Angle                               __________________________________________________________________________    F2-2                                                                              1.62                                                                              3.15 2.27                                                                             0.97 417                                                                              692                                                                              170  5.2                                                                              5 7500 60                                  F2-1                                                                              1.51                                                                              Control      167                                                                              477                                                                              170  -- --                                                                              --   --                                  J-2 1.57                                                                              3.74 2.45                                                                             0.76 302                                                                              690                                                                              200  4.4                                                                              7 8400 60                                  F4-1                                                                              1.55                                                                              3.58 2.42                                                                             0.86 285                                                                              712                                                                              200  4.0                                                                              7 8400 60                                  __________________________________________________________________________

The preferred embodiment or best mode for a particular application, ofcourse, depends on not only the degree of cooling and rib formationformed but also counter-balanced against the complication or the rate ofspeed obtainable with the varying modes for accomplishing the variousspecies of the present invention.

For example, in FIG. 3 a water wick made of felt, cotton, or syntheticfabrics which are water absorbent can be fed by water supplies tochannel 80 engaging the outer surface of the film 26 at points 72 and 74to cool narrow strips of film to thicken the same. The wicks contactingthe film in close proximity to one or more air bearings 20 or 22. Inthis arrangement, a water delivery system must be provided for thewicks. Particularly, the water wicks 68 or 70 may be round, rectangular,or curved. The wick width or diameter may be from 0.01 inch to 0.50 inchand preferably 0.10 inch to 0.30 inch. The wicks may be optionallymounted in an air bearing flush with the air bearing or extending up to0.125 inch. The spacing between the wicks may range from 0.30 inch to3.0 inch with the preferred range being 0.60 inch to 1.5 inches. Theexpansion of the tube at the wicks should be in the range of -10% to 75%of the total expansion, with the preferred range being -10% to 25% ofthe total expansion. The wicks may be vertical and stationary producingvertical ribs in the film, set at an angle and rotating for diagonalribs, or two sets of wicks set at opposed angles may be counter-rotatedto produce a mesh film.

Metal shoes (not shown) may replace the water wicks of FIG. 3 and can belocated either internally or externally of the film. Such metal shoesmust be cooled by known heat exchange methods and need to have an airbearing in close proximity to maintain the film in proper contact withthe metal shoe while avoiding snagging and sticking. The shoe or shoesand adjacent air bearings are brought into contact with the film, withthe cooled metal shoe providing the selective cooling of the film, theshoes are carried by rotating rings in a manner similar to the previousembodiments disclosed. Particularly, the shoe may be round, rectangular,or curved.

The shoe width may be from 0.010 inch to 0.50 inch, preferably 0.10 inchto 0.30 inch. The shoes may actually be inserted in an air bearing (asin slits 102 and 104 of FIG. 6, for example) flush with the air bearingsurface or extending up to 0.125 inch beyond the surface. The spacingbetween the metal shoes may range from 0.30 inch to 3.0 inches with thepreferred range being 0.60 inch to 1.5 inches. The expansion of the tubeat the metal shoes should be in the range of -10% to 75% of the totalexpansion, with the preferred range being -10% to 25% of the totalexpansion. The shoes may be vertical and stationary producing verticalribs on the film, set at an angle and rotating together for diagonalribs or two sets with opposite angles and counter rotation for meshpattern. Maintaining the shoe at a temperature below the dew pointprovides a wetted shoe cooling method. When operating below the freezingpoint of water, an ice film tends to form on the shoes resulting in ashoe that "skates" across the film surface. This provides minimalfriction and extreme cooling.

Many factors can vary the degree and sharpness of the rib profile and ofthe tear strength. Again, this is an arrangement whereby simple aircooling against an adjacent air bearing is employed. Increasing the airvelocity of the cooling nozzles from 9400 fpms to 13,500 fpms canincrease by more than 20 percent the tear strength of the resulting filmat least in the machine direction. It should be pointed out there areother examples of which the above are typical. Various factors changedas conditions were changed but the overall results typified by the aboveare what can be commonly expected by applications of the principles ofthe present invention.

Tear strength of thermoplastic materials which are ribbed according tothe principles of the present invention has a direct relationship to ribsharpness. By use of the present invention, a high degree of ribsharpness can be obtained. The relationship of rib sharpness to tearstrength is, as the height to width ratio increases, the tear strengthcan advance to over 100 percent of what it would have been otherwise butfor the present invention. The limitation on rib height is primarilyattributed to a thickness which will not interfere with the packing ofthe bags into a box. A certain degree of compactness is necessary formarket purposes. The present invention has been found to provide a highdegree of rib sharpness while maintaining necessary compactness. Atypical rib made by this invention for a film having a nominal thicknessof 1.5 mils could have a rib height of about 3 mils, and a width of fromabout 40 to 120 mils.

While certain representative embodiments and details have been shown forpurpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and applications can be madetherein without departing from the spirit and scope of the invention.For example, the speed of rotation of the cooling mechanisms, size andshapes of the nozzles can be modified to fit particular resin materialsor combinations of resin materials being extruded and the operatingconditions under which the materials are extruded. Additionally, theparticular spacing of the ribs from one another, the shapes of thediamonds between the ribs can be best determined for a particularapplication by those skilled in the art applying the principles of thepresent invention. Likewise, the layers of a coextruded film may be madesuch that the ribbed layer is particularly heavily pigmented but thinnerthan the other layer or layers, so that the ribs stand out as adistinctly contrasting color. Much flexibility in making novel productsis possible following the principles of the present invention. Having 30or more ribs per foot of film width is feasible, for example.

What is claimed is:
 1. A method for the forming of a thermoplastic filmhaving a strength imparting ribbed mesh pattern, the steps of the methodcomprising extruding through a die a heat-plastified synthetic resinouscomposition in the form of a tube having generally radial symmetry aboutthe axis of extrusion, passing the tube while still in a heat-plastifiedcondition past a cooling mechanism having a defined periphery, saidmechanism having a plurality of counter-rotating elements for impingingcooling means on the tube, fixedly spacing said film with respect tosaid cooling means, impinging said cooling means on said film, saidcooling means imparting sharp ribs on the film body, said tube beingformable into a tough film having a ribbed mesh pattern formed thereon.2. The method of claim 1 wherein said cooling mechanism elements arecounter-rotated with respect to one another at about the same speed toimpart essentially a uniform cross-ribbed pattern on the tube body. 3.The method of claim 1 wherein the cooling means is angled with respectto the face of the die to increase the sharpness of the rib formedthereby.
 4. The method of claim 1 wherein the cooling means compriseseither cooled gas, vapor mist, snow, liquid, or a combination thereof.5. The method of claim 1 wherein after the tube exits the die but beforeit passes the rotating cooling mechanism, biaxially stretching the tubewhile passing the tube over a generally circular gas-bearing meanslocated adjacent said die and having a diameter greater than thediameter of the tube as it is initially extruded.
 6. The method of claim5 wherein the cooling mechanism is located closely adjacent thegas-bearing means.
 7. The method of claim 6 wherein said tube is passedover a subsequent gas-bearing means for further cooling after it passessaid cooling mechanism.
 8. An apparatus for the forming of athermoplastic film having a strength imparting ribbed mesh patternthereon, said apparatus comprising a die for extruding a tubularthermoplastic extrudate, a cooling mechanism located adjacent said dieand defining a generally circular periphery with respect to the tubularextrudate, elements located about said mechanism including means forimpinging a cooling means upon the surface of said tubular extrudate,means for counter-rotating said elements, and means for fixedly spacingthe film with respect to said cooling means, whereby a cross-ribbed meshpattern is produced on said film when said cooling means is impinged onsaid film with said apparatus.
 9. The apparatus of claim 8 wherein saidelements define elongated orifices, the axis of each of said orificesbeing at an angle of about 45°±20° to the face of said die.
 10. Theapparatus of claim 8 wherein the nozzle face is at an acute angle to thesurface of the extrudate.